With Power CMS each page you create will be stored in the db. You can view the contents by putting in the code in the developer area on any end page the user will visit. So the archiving functionality is already a part of PowerCMS. The part that would not be done by Power CMS is to automatically update the page with the new content.
You could edit the current mini site, say Winter 09, and copy the content, then insert this into a new page that will serve as the archive page and update what was the Winter 09 page to be the Spring 10 page.
Or you could just add the new pages to the PowerCMS whenever you need to then update the code reference on the page to use this new page. You could then add the old page reference to the list of archive pages.
Neither option is fully automatic but it can simplify the process.